Field of the Invention
The present invention relates to a die cushion device of a press machine, and more particularly to a die cushion device of a press machine, with a plurality of cushion pads for one press machine.
Description of the Related Art
Heretofore, this kind of die cushion device has been disclosed in Japanese Patent Application Laid-Open No. 06-000543 (Patent Literature 1), Japanese Patent Application Laid-Open No. 07-100552 (Patent Literature 2), and Japanese Patent Application Laid-Open No. 2006-192481 (Patent Literature 3).
Patent Literature 1 describes a die cushion device that includes a plurality of divided cushion pads each of which supports a lower die from below through a cushion pin. Each of pad members is connected to a rack rod that is connected to a servo motor provided in each the pad members through a reduction gear train. A numeric value control device provides position control and torque control to each of servo motors to obtain cushioning action.
In an embodiment of the invention described in Patent Literature 1, four divided cushion pads are used, and driving force can be transmitted to the pads by respective four pairs of rack-and-pinion mechanisms, each of which is driven by a servo motor. Two pairs of the rack-and-pinion mechanisms of the four pairs of rack-and-pinion mechanisms are positioned in a side-to-side direction, and a joint with a minimum backlash connects between shafts of the respective pinions. Two pairs of the rack-and-pinion mechanisms of the four pairs of rack-and-pinion mechanisms are also positioned in a vertical direction, and intermediate gears in a reduction gear train are engaged with each other with a minimum backlash (refer to the paragraph [0007] in Patent Literature 1). That is, Patent Literature 1 shows that the four pairs of rack-and-pinion mechanisms are mechanically synchronized with each other with minimum backlashes.
Patent Literature 2 describes the invention that provides a die cushion device of a press, in which a pad body is elastically supported by a cushion cylinder, and an NC cushion cylinder to which numerical control is provided controls cushion force. The pad body is divided into a plurality of pad members, and a part of the pad members is coupled with each other by a coupler to form a flexible structure. In addition, one cushion cylinder and one NC cushion cylinder are provided for each of the pad members.
Patent Literature 3 describes a die cushion device that includes a plurality of small pads that receives pressing force of a slide through a cushion pin, a large pad that supports the plurality of small pads, and an urging force generating device that moves up and down the large pad while generating upward urging force against the pressing force.